Resistance unit



Patented Dec. 1, 1936 UNITED STATES TENT OFFICE REsisTANca UNIT Ware Application May 17, 1932, Serial No. 611,850

20 Claims.

This invention relates to electric resistors in general and more particularly to fixed current limiting resistors which are adapted for use on comparatively high voltage systems.

It is one of the objects of the present invention to provide a sturdy resistor unit which may be mounted outdoors and wherein the resistance element is protected from vermin or other animal life, dust, moisture or the like.

It is an object of the present invention to provide a current limiting resistor of a form suitable for convenient manufacture and assembly, as well as for convenient repair and replacement.

The chief object of the present invention is to provi-de a resistor ci improved construction, particularly adapted to facilitate the dissipation of heat. Thereby compactness is obtainable without sacricing permanence or weather resisting qualities. Also, due to high heat dissipating ability, such resistors may be placed in power circuits, as in a transformer circuit carrying 1), l5 or more amperes.

In carrying out the above object we have provided different structural members to perform different functions. Thus the resistor supporting sleeve may be made of a material or in a form to adapt it to expansion or contraction incident to variation of temperature due to current flow. The supporting member may be made of suitable structural material or form to adapt it to perform its mechanical supporting and electrical insulating function without being subject directly to the heat of the resistor. The enclosing sleeve is made of a vitreous material, for example, glass, which does not deteriorate by weathering or electrical leakage, and is not subjected to the expansion and contraction of the part which directly supports the wire resistance. In one form of the present invention the ends of the unit are provided with heat radiating iianges or fins. In another embodiment of the present invention the unit is so constructed as to permit the natural circulation of air therethrough while maintaining the resistance wire itself closed off from the atmosphere. This unit comprises a vertically extending hollow cylindrical insulating core on the outsi-de of which is wound a wire resistor which is protected from the atmosphere by a glass sleeve surrounding the unit and end members closing off the space between the sleeve and the core at the ends while leaving the hollow interior of the 'cyiindrical insulating core open. As the unit heats, convection currents will circulate through g the core cooling the inside thereof while heat is at the same time being radiated outwardly of the outer sleeve.

The attainment of the above and further objects of the present invention will be apparent from the following specication taken in con- 5 junction with the accompanying drawing forming a part thereof.

In the drawing:

Figure 1 is a half-sectional View of one form of the present invention; 0

Figure 2 is a half-sectional view of a hollow core type of unit embodying the principles of the present invention; and

Figure 3 is a top view of the unit shown in Figure 2.

The resistor unit shown in Figure 1 comprises a core Sii of porcelain or other suitable ceramic insulation having heat insulating members 8 |-82 secured to the ends thereof in any suitable manner, as by means of screws threaded directly into tapped holes in the insulator or into tapped inserts cemented or otherwise secured in sockets formed in the core 80. The core provides the mechanical strength for the unit and xedly spaces and supports heads 81 and 88. An insulating sleeve or cylinder 85 surrounds the core S0 and rather loosely embraces the insulating members 8i-82. The sleeve 85 has suicient play with respect to the plates 8| and 82 and adjacent parts as to permit free contraction and expansion of the sleeve due to thermal changes caused by variations of current in the resistance Wire 86. The sleeve is thus free to contract and expand not only axially, but also radially. The sleeve 85 is provided with a helical groove in which lies a resistor wire 86 that comprises a resistance wire such as nichrome or chromel wound into an open helix of small diameter, the convolutions of the coil being spaced apart so as to avoid contacting with one another, particularly when they are wound in place in the helical groove in the member 35. The end closure members comprise castings 8`l-G8 of bronze or other suitable conducting material secured in place by means of screws 89 threaded into inserts in the heat insulating members 8l-82. The flanged heads 8l and 88 provide annular seats containing suitable gaskets for maintaining a substantiall;r tight connection with the glass enclosing sleeve 6. This sleeve is supported radially and axially on said flanged heads with suitable radial and axial gaskets interposed. Plates 90 of brass or other suitable conducting material are interposed between the end members 8l and the members 8|-82. These brass plates comprise anchors for the ends of the resistor wire 85. Heat radiating discs 92-92 are secured to each of the end castings 81-08. The discs have outwardly extending fins that afford good heat radiating surfaces and thereby reduce the temperature of the ends of the resistor unit. While only two heat radiating discs have been herein shown at each end of the unit it is to be understood that a greater or lesser number may be used as desired, or the discs may be entirely omitted from one end Without departing from the spirit of the present invention.

Reference may now be had to Figures 2 and 3 wherein a different form of resistor unit is shown. The resistor wire is indicated at |00 and it is wound in a helical groove formed on the outer side of a hollow cylindrical sleeve of insulation |0| of lava or the like. The upper closure member comprises a rim |02 of somewhat larger diameter than the diameter of the core. The rim is slipped over the end of the core and constitutes a terminal for the Wire |0|. The end of the wire |0| is secured in a terminal clip |03 formed on the inside of the rim |02, said Wire being firmly clamped in place by means of a screw |04. The end of the rim |02 is provided with a circular groove that fits over the end of a glass sleeve |06 and is sealed thereto by means of a suitable packing |01 of asbestos, rubber, or the like. The rim |02 is held in place upon the insulating core |0| by means of a pair of semicircular members |08 and |09 that together comprise a circle fitting into a groove in the end of the core |0|. The split ring members |08 and |09 are secured to the continuous ring |02 by means of a number of screws I2 thereby holding the ring |02 against Withdrawal. A suitable sealing gasket or packingis interposed between the ring members |08- |09 and the core |0| to seal the end of the chamber formed between the core |0| and the glass sleeve |06.

The ring |02 is provided at one end with means for mounting the same. This means comprises a pair of arms I5 and l I6 formed integrally with the ring |02 and united by an integrally formed portion I1 that is adapted to seat on an insulator and be secured thereto, as indicated in Figure 9. The portion l l1 comprises a terminal lug for extending the circuit from the resistor unit.

The lower end of the core |0| is provided with a closure cap of a construction substantially identical to that at the upper end of the core. A further description of this cap need therefore not be given.

The unit shown in Figure 9 is preferably mounted in a vertical position on a pair of insulators, as shown. These insulators hold the rings |02-l 02 in definite spaced relation independently of the glass sleeve |06. Air will naturally circulate through the inner core and effectively cool the same. At the same time there is the natural dissipation of heat through the outside of the glass sleeve |06. By this arrangement a. comparatively large current can be carried without overheating the resistance unit.

In compliance with the requirements of the patent statutes we have herein shown and described a few preferred embodiments of our invention. It is however to be understood that the invention is not limited to the precise constructions herein set forth, same being merely illustrative of the principles of the invention.

What we consider new and desire to secure by Letters Patent is:

1. A high tension current limiting resistor,

comprising the combination of a pair of metallic end pieces, an inner core of electrical insulation forming a rigid connection between the end pieces, a sleeve of heat resistant insulation surrounding the core and being supported to permit free expansion and contraction with respect to the said end pieces independently of the expansion and contraction of said core, and a resistance wire Wound on said sleeve.

2. A high tension current limiting resistor, comprising the combination of a pair of metallic end pieces, an inner core f electrical insulation forming a rigid connection between the end pieces, a sleeve of heat resistant insulation surrounding the core and being supported to perreous weather resistant sleeve spaced radia1lyfrom the resistance wire and sea-led to said metallic end pieces to provide a non-deteriorating enclosure for said resistance Wire.

3. A resistor comprising an inner supporting core and, surrounding the same, a sleeve of insulation, a wire resistor mounted on the sleeve. an outer sleeve of insulation surrounding the irst sleeve, end caps secured to the inner core and forming a seal with the outer sleeve, and a metallic end plate comprising a terminal interposed between the rst named sleeve and at least one of the end caps.

4. A resistor comprising an inner supporting core and, surrounding the same a sleeve of insulation, a wire resistor mounted on the sleeve, an outer sleeve of insulation surrounding the rst sleeve, end caps secured to the inner core and forming a seal with the outer sleeve, a metallic end plate comprising a terminal interposed between the first named sleeve and at least one of the end caps, and a heat insulating member interposed between the end plate and the supporting core.

5. A resistor unit comprising a pair of concentric hollow cylindrical insulating members, a resistor wire between the two, closure members at the ends of the two rst mentioned members insulated from one another and closing the space between the two cylindrical members, the ends of the inner cylindrical member being open to atmosphere to permit the natural circulation of air therethrough.

6. A resistor unit comprising a hollow cylindrical core of insulation open to the atmosphere at the top and bottom to permit a natural circulaton of air therethrough from outside the unit, a resistance wire on the outside of the core, a sleeve surrounding the core and spaced therefrom, and end closure members securing the sleeve to the core and closing off the space between the sleeve and the core, said end members comprising terminals for the ends of the resistance wire.

7. A resistor unit comprising a hollow cylindrical core of insulation open to the atmosphere at the top and bottom to permit a natural circulaton of air therethrough from outside the unit, a resistance wire on the outside of the core, a sleeve surrounding the core and spaced therefrom, and end closure members securing the sleeve to the core and closing oif the space between the sleeve and the core, said end members comprising terminals for the resistance wire and having mounting means extending therefrom for mounting the unit.

8. A resistor unit comprising a hollow cylindrical core of insulation open to the atmosphere at the top and bottom to permit a natural circulation of air therethrough from outside the unit, a resistance wire on the outside of the core, a sleeve surrounding the core and spaced therefrom, and end closure members securing the sleeve to the core and closing ofi" the space between the sleeve and the core, said end members being secured to the core by means including split rings inserted into peripheral grooves in the core and secured to the end members.

9. An electrical device comprising a core of insulation having external peripheral grooves at the ends thereof, a sleeve surrounding the core and spaced therefrom, a wire resistor disposed in the space between the core and the sleeve, end members securing the sleeve to the core and closing ofi the space between the sleeve and the core, said end members being secured to the core by means including splitirings inserted into the peripheral grooves and secured to the end members.

10. A device of the class described comprising a hollow cylindrical insulating member open to atmosphere at both ends, a pair of metallic clamps embracing the opposite ends thereof` and comprising terminals, a coil wound around the cylindrical member between the clamps and connected at its ends to the respective clamps, and a tube of insulation spaced from the coil and surrounding the insulating member and sealed to the two clamp members.

11. In combination, a substantially cylindrical body of refractory insulation having peripheral grooves at its ends, a resistor on the body between the grooves, a sleeve surrounding the body of insulation and terminating in rims at its two ends, and split rings ext-ending into the grooves and removably secured to the rims, whereby the rims are held by the rings and hold the rings against retraction from the grooves.

12. A resistor unit comprising a hollow tubular body of frangible insulation, a resistor wire wound around the outside thereof, a glass tube surrounding the insulation and spaced from the resistor wire, fianged end members comprising terminals at the opposite ends of the body of insulation and s-ealing the space between the glasss tube and the body of insulation` a yielding packing between the end members and the glass tube maintaining the seal between the end members and the glass tube while permitting a limited relative shifting between them under expansion and contraction incident to thermal changes and means independent of the glass tube for holding said end members in fixed insulated relation, said hollow tubular body being mounted on said end members with suflicient free play to permit thermal contraction and expansion.

13. A resistor unit comprising a hollow tubular body of frangible insulation, a resistor wire wound around the outside thereof, a glass tube surrounding the insulation and spaced from the resistor wire, the space between the resistor and the glass tube being filled with a gaseous medium to facilitate the dissipation of heat radially outwardly of the unit, iianged end members comprising terminals at the opposite ends of the body of insulation and sealing the space between the glass tube and the body of insulation, means for mounting the end members in place comprising split rings separate from the end members and radially contractible into indentations in the body of insulation and held against radial expansion by screw means securing the split rings to the end members, said hollow body of insulation extending through the two end members and being open at both ends to permit a natural circulation of cooling air therethrough, and a yielding packing between the end members and the glass tube maintaining th-e seal between the end members and the glass tube while permitting a limited relative shifting between them under expansion and contraction incident to thermal. changes.

14. A current limiting resistor for high tension power circuits, comprising a sleeve of insulating material, a pair of metallic members forming electrical terminals and providing radial and axial support for said sleeve with sufficient play relative to said metallic members to permit free thermal contraction and expansion of said sleeve, a resistance wire supported upon a cylindrical surface of the sleeve and being connected electrically to said members, said members having flanges, a glass sleeve extending between said flanges to form an enclosure for said resistance wire, yielding packing between said iianges and said glass sleeve, and insulating means rigidly supporting said members in spaced relation independently of said glass sleeve and of said sleeve of insulating material.

15. A current limiting resistor for high tension power circuits, comprising a sleeve of insulating material, a pair of metallic members forming electrical terminals and providing radial and axial support for said sleeve said sleeve having suiiicient free play relative to said metallic members to permit thermal contraction and expansion, a resistance wire supported upon a cylindrical surface of the sleeve and being connected electrically to said members, said members having flanges, a glass sleeve extending between said iianges to form an enclosure for said resistance wire yielding packing between said flange and said glass sleeve, insulating means rigidly supporting said members in spaced relation independently of said glass sleeve and of said sleeve of insulation, and heat radiating flanges thermally in engagement with said members for dissipating heat therefrom.

16. In a device of the class described, the combination of a sleeve of heat resistant insulation, a pair of rings loosely embracing the sleeve adjacent its ends to permit thermal expansion and contraction of the sleeve relative to said rings, a second sleeve of insulation held in substantially coaxial position with respect to said first sleeve by said rings, a metallic resistor mounted on said first sleeve and enclosed by said sleeves and rings, said rings serving as terminals for said resistor, and means for rigidly supporting said rings in spaced relation, said first sleeve extending through and projecting beyond at least one of said rings.

17. In a high tension current limiting resistor, the combination of a pair of spaced metallic end pieces, a sleeve of heat resisting insulation having a resistance wire wound thereupon, said wire being connected to said end pieces, said sleeve being mounted loosely with respect to said end pieces to permit expansion and contraction due to thermal changes produced by variations of current flow through the wire, and rigid supporting means including insulation comprising a solid block of porcelain providing adequate creepage distance for the high tension current, said means constituting the sole means for holding the end pieces in fixed position.

18. In a high tension current limiting resistor,

the combination of a pair of' spaced metallic end pieces, a sleeve of heat resisting insulation having a resistance wire wound thereupon, said wire being connected to said end pieces, said sleeve being mounted loosely with respect to said end pieces to permit expansion and contraction due to thermal changes produced by Variations of current now through the wire, rigid supporting means including insulation providing adequate creepage distance for the high tension current, said means holding the end pieces in xed position, and a vitreous Weather resistant sleeve spaced radially from the resistance wire and yieldingly sealed to said metallic end pieces to provide a non-deteriorating enclosure for said resistance wire.

19, In a high tension current limiting device, the combination of a pair of annular metallic end pieces, a resistance wire connecting said pieces,

a tubular electrical insulating member open atl its ends for ventilation and being adapted to withstand the heat of the resistance wire and being held loosely by said end pieces to permit its independent contraction and expansion due to temperature changes, and means independent o1 the said member and being disposed wholly at one side of said member forming the sole support for holding the end pieces in fixed and insulated relation to each other.

20. In a high tension current limiting device, the combination of a pair of metallic end pieces, a resistance wire connecting said pieces, an electrical insulating member adapted to withstand the heat of the resistance wire held loosely by said end pieces to permit its independent contraction and expansion, due to temperaure changes, means independent of the said member forming the sole support for holding the end pieces in fixed and insulated relation to each other, and a sleeve of vitreous weather resistant material yieldingly sealed to the end pieces and cooperating with the end pieces to form an enclosure for said wire resistor.

HUGH A. TRIPLETT. ALLAN RAMSEY. 

